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Chapter: Application End Classes

Application End Classes

Application end
classes are unlike most components in that they are not related to a call
session. Application end classes are instead associated with a particular
application and are executed when the application itself is taken down or
updated. Currently, only the Java API can construct code to run when an
application starts.

An application can
define in its application settings any number of application end classes. VXML
Server will execute the classes sequentially in the order they appear in the
application’s settings. By conforming to this order, a developer can create an
application end class that stores information that can then be referenced by
subsequent end of application classes.

Unlike application
start classes, an error in one application end class does not cancel the
application release, once started the application will be released no matter
what occurs. Should an error occur in an application end class, an error event
will be thrown for any error loggers to report.

There are four
situations where the application end class is run:

The application
server is shut down. VXML Server is configured to shut down all of its own
operations as well as shut down each individual application by running their
application end classes.

The VXML Server
web application is restarted. Most application servers provide the ability to
restart just a certain web application running within it rather than restarting
the entire application server. The act of restarting the web application that
defines VXML Server will prompt it to initiate the application unloading
process, including calling its application end classes just like an application
server restart.

An application is
released after the VXML Server has started. Using the release administration
scripts, an application can be released while the system is actively handling
calls to other applications. VXML Server will first run all application end
classes for the application and then release it from memory.

An application is
updated. The process of updating an application prompts VXML Server to create a
new instance of the application in memory, while keeping the old instance in
memory long enough for all existing callers to complete their calls. Once all
calls have completed with the old instance, that instance’s application end
classes are run.

An application end
class only has access to the Global API, which allows for the creation of
global and application data. It does not have access to the Session API because
it is not run within a call session and is associated only with an application,
not a call.

The main purpose for
an application end class would be to perform cleanup operations for an
application. Typically this would involve closing database connections or files
that were opened by an application start class or by code run within calls to
the application. Application end classes have the ability to create application
or global data, though the concept of creating data right before the
application is released would seem pointless. The one situation where this
would be useful would be to set data that a subsequent application end class
could use. For example, an application start class could open up a database
connection and store it in global data so that all applications deployed on
VXML Server could utilize the connection. This connection would need to be
closed, but if there are multiple applications with multiple application end
classes, the desire would be to close the connection by the last application to
be released, in case the application end classes need to use the connection.
Each application start classes could increment an application count value
stored in global data that the application end classes would decrement. The
application end class that yielded a zero would know that it was the last
application released and so close the database connection.

The application end
class action is built by implementing the Unified CVP class
EndApplicationInterface found in the
com.audium.server.proxy package. It contains a single
method named
onEndApplication that is the execution method for the
application end class. This method receives a single argument, an instance of
ApplicationEndAPI. This class belongs to the Global API
and is used to access and create application data and global data (see the
User Guide for Cisco Unified
CVP VXML Server and Unified Call Studio for details on application and
global data). The method does not have a return value. It is expected that
should an unrecoverable error occur, the application end class will throw an
AudiumException.